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GNU Compiler Collection (GCC) Internals

4. Language Front Ends in GCC

The interface to front ends for languages in GCC, and in particular the tree structure (see section 7. Trees: The intermediate representation used by the C and C++ front ends), was initially designed for C, and many aspects of it are still somewhat biased towards C and C-like languages. It is, however, reasonably well suited to other procedural languages, and front ends for many such languages have been written for GCC.

Writing a compiler as a front end for GCC, rather than compiling directly to assembler or generating C code which is then compiled by GCC, has several advantages:

• GCC front ends benefit from the support for many different target machines already present in GCC.
• GCC front ends benefit from all the optimizations in GCC. Some of these, such as alias analysis, may work better when GCC is compiling directly from source code then when it is compiling from generated C code.
• Better debugging information is generated when compiling directly from source code than when going via intermediate generated C code.

Because of the advantages of writing a compiler as a GCC front end, GCC front ends have also been created for languages very different from those for which GCC was designed, such as the declarative logic/functional language Mercury. For these reasons, it may also be useful to implement compilers created for specialized purposes (for example, as part of a research project) as GCC front ends.